1. Field of the Invention
The present invention pertains in general to a sewing machine with a lower feed dog movable in vertical and horizontal directions and in particular to a sewing machine where the lower feed dog can move either horizontally and vertically, or only horizontally.
2. Background Art
A sewing machine of this design has been known from West German Patent Specification No. DE-PS 21,08,309 and its parallel U.S. Pat. No. 3742880. It has a combined feed device, which consists of a lower feed dog and a needle feed device, in which an oscillating shaft controlling a needle bar oscillating frame is connected to an oscillating shaft moving a feed dog holder to and fro in a horizontal plane. The oscillating movements of the oscillating shaft are derived from a feed cam and the amplitude of these movements can be adjusted by means of a stitch length regulating device. Besides the horizontal reciprocating movements, vertical lifting movements are imparted to the lower feed dog by a driving cam via a cam rod and a crank mechanism, so that the lower feed dog performs a tetragonal movement. This combined feed device guarantees the displacement-free sewing together of a plurality of fabric layers.
A band strip bordering apparatus participates in the horizontal movements of the feed dog, and folds a bond strip in the shape of a U around the edges of the fabric. When fabric edges are bordered with a band strip, which is fed in and sewn on, the lower feed dog must not perform any vertical movements. In this machine, the lifting drive mechanism, the driving cam, and the cam rod must be removed. This takes very much time, when the sewing machine is to be used for bordering operations with the attached band strip bordering apparatus. For use in normal sewing operations, it is necessary to reinstall the lifting drive mechanism.
As an alternative, it is possible to use a second sewing machine in which only horizontal pushing movements, but no vertical lifting movements, are imparted to the lower feed dog. Such a sewing machine has been known from West German Offenlegungsschrift No. DE-OS 18,09,0979 and its parallel U.S. Pat. No. 3467039. However, this sewing machine is suitable only for certain sewing operations.
From FR-A-926 213 the insertion of a coupler in the hoist drive of the material slider of a sewing machine for the neutralization of the vertical motion of the material slider is known. However, the printed material does not indicate for which purpose this should be used.